What it is
Boats run the 200-odd kilometres between Luxor and Aswan in three or four nights, stopping at the temples on the bank: Esna, Edfu, Kom Ombo. Standard cruisers are floating hotels of 50 to 150 cabins with pools on the roof. Dahabiyas are small sailing boats, usually six to twelve cabins, that move more slowly and moor in quieter places.
Why go
Those riverside temples are awkward to reach by road and easy from the water. It also breaks up a schedule that is otherwise several hard days of walking around ruins.
When to go
October to April. The direction matters less than the schedule: Luxor to Aswan is upstream and usually slightly longer, Aswan to Luxor faster. Cruisers moor several abreast at busy stops, so a window can look straight into another boat's cabin. Boats can sit idle when the Esna lock is congested. In peak season the temples are busiest when every boat arrives at once, in the middle of the morning.
Most people stay 3-4 nights.